Abstract

Marine phytoplankton are microscopic algae that form the basis of the marine food web and play an important role in many biogeochemical cycles - for example, carbon fixation: phytoplankton are estimated to produced half of the world's oxygen. Their contribution to biochemical cycling depends significantly on the complex interactions between environmental conditions and metabolism. Although temperature is known to significantly affect phytoplankton growth and community composition we have a limited understanding of the impact of temperature on phytoplankton metabolism. To investigate this relationship we employed an integrative approach combining metatranscriptomes from eukaryotic phytoplankton from distinct latitudinal temperature zones, biochemical data and cellular physiology and growth strategies in a global model. Analysis of the metatranscriptomes revealed a strong negative correlation between the proportion of transcripts encoding for ribosomal proteins and in-situ
temperature. This relationship was subsequently confirmed on model phytoplankton under laboratory conditions at both the transcript and protein level. A translational efficiency experiment revealed that as temperature decreases the rate of protein synthesis also decreases, despite the increase in the number of ribosomes and their associated rRNAs. Global phytoplankton cellular resource allocation models show that this has implications for the Redfield ratio (in particular the ratio of nitrogen (N) to phosphate (P)). Under increasing temperatures the amount of phosphate-rich ribosomes will be reduced leading to a higher N:P ratio, in turn leading towards an increased demand for nitrogen and potentially leading toward nitrogen limitation.